In Korean utility model registration No. 221534, there were disclosed a bone conduction telephone for those who have impaired of hearing and a hearing aid vibrator by using a piezoelectric device as described above.
Referring now to FIG. 1, which shows the bone conduction telephone and the hearing aid vibrator using the conventional piezoelectric device, there were disclosed a bone conduction telephone and a hearing aid vibrator using the piezoelectric device, comprising a piezoelectric device 100 for generating physical vibration according to the application of electrical voice signal, vibrating plates 101 disposed at both end sides of the piezoelectric device 100, which apply the electrical signal to the piezoelectric device 100 through a conducting wire 103, a front contact portion 104 mounted closely and connected to an electrode plate 102 for transmitting the vibration to the outside, and a cover 105 for protecting and supporting the piezoelectric device, whereby the piezoelectric device 100 generates vibration conforming to the voice frequency by means of the piezoelectric effect, according to the voice signal applied through both the vibration plate 101 and the electrode plate 102 to thereby transmit the generated vibration signal to the outside.
However, since the bone conduction telephone and the hearing aid vibrator using the subminiature vibrator and the piezoelectric device should employ high impedance and high input voltage, the output acoustic pressure was low and it was difficult to make them compact, so a lot of problems were produced in implementing it actually.
Furthermore, a subminiature acoustic vibrator was disclosed in Korean Patent Laid-Open Publication No. 2001-0106898.
Reviewing the subminiature acoustic vibrator with regard to FIG. 2, when the electric current is applied to a terminal portion (not shown) from the outer electric power supply source to thereby supply it to a voice coil 110, the voice coil 110 induces the change of magnetic field from the electrical energy of voice signal. In other words, when the electric current is applied to the voice coil 110, magnetic field is produced between the voice coil 110 positioned in the clearance of the magnetic circuit comprising a yoke 112, a magnet 111, and an upper plate 113, the magnetic circuit comprising the yoke 112 is made to vibrate in the upward and downward directions by means of the Fleming's left hand law, through the interaction between the magnetic field in the magnetic circuit, the vibration contact portion 114 connected to the yoke 112 is made to vibrate concurrently, and the vibration of the vibration contact portion 114 is transmitted to a head portion of a human being, so that those who impaired of hearing can hear the bone conduction sound.
However, according to the bone conduction speaker, the yoke 112, the magnet 111, and the upper plate 113 are operated as parts for forming the magnetic field and vibrated in the upward and downward directions, so that high driving voltage is required to vibrate the yoke 112, the magnet 111, and the upper plate 113. Accordingly, there is caused a problem of requiring a large amount of electric power consumption.
In this regard, a subminiature bone conduction speaker using a vibrating plate, and a mobile phone with the same have been disclosed in Korean patent registration No. 0378156.
Reviewing the subminiature bone conduction speaker using a vibrating plate, which is a conventional bone conduction speaker, and a mobile phone with the same with reference to FIG. 3, a projection 120, an auxiliary vibrating plate 122, and a voice coil 123 are mounted to a vibrating plate 121, so that the mastoid 120, an auxiliary vibrating plate 122, and the voice coil 123 are constructed to vibrate by using the elasticity of the vibrating plate 121 resulting in performing of the bone conduction, after the magnetic force applied to the voice coil 123 is affected by a ring type magnet 124.